The present invention pertains generally to the field of angioplasty and, in particular, to a form of angioplasty involving lesion cooling.
Conventional angioplasty has been preformed for several decades, prolonging the lives of an ever increasing number of patients. Angioplasty procedures involves the dilatation of a balloon placed across a lesion in a coronary artery. Dilatation of the balloon in turn dilates the lesion, opening the artery for increased blood flow. In some cases, however, the goal of the angioplasty procedure is, in whole or in part, frustrated by complete or partial reclosure of the artery at the lesion. Two mechanisms are believed to be principally responsible for reclosure of the artery, these are restenosis and recoil. Restenosis is believed to be caused by continued growth or regrowth of the smooth muscle cells associated with the lesion. Recoil is in part a mechanical process involving elastic rebound of the dilated lesion.
Several means have been disclosed for addressing the problem of restenosis. These include, among others, radiation treatments to slow or prevent smooth muscle cell proliferation associated with the restenotic process. Certain drug therapies have been proposed to prevent or slow restenosis.
Several means have also been developed to address the issue of recoil. One of the more significant developments in this area has been stents, which can be permanently deployed to mechanically hold open lesions. Although stents have been found to be highly effective, they may irritate the wall of a artery in which they are implanted. Some believe that this may encourage limited restenosis. Warming of the lesion during dilatation has also been disclosed to prevent or slow recoil. Warming the lesion is believed to soften the lesions such that it may be xe2x80x9cremodeledxe2x80x9d that is, thinned under low pressure. Heating of the lesion, however, is believed to cause an injury response which may cause some restenosis.
The present invention is directed at an apparatus and method for performing angioplasty and preventing or slowing the post-procedure reclosure of a dilated lesion. The present invention cools the lesion to prevent or slow reclosure by the mechanisms of restenosis or recoil. A cryoplasty catheter is provided to cool the lesion to aid in remodeling the lesion to prevent or slow recoil. The present invention can also be used to cool the lesion to freeze a portion of the lesion tissue. This is believed to kill cells within the lesion which would promote restenosis.
A preferred embodiment of the cryoplasty catheter in accordance with the present invention includes a shaft having proximal and distal ends. The shaft defines an inflation lumen, coolant intake lumen and exhaust lumen therethrough. Each lumen has a proximal and distal end proximate the proximal and distal ends of the shaft respectively. A dilatation balloon is disposed at the distal end of the shaft and is in fluid communication with the inflation lumen. A chamber is disposed within the balloon and is in fluid communication with the intake and exhaust lumens. A source of coolant is connected to the proximal end of the shaft in fluid communication with the coolant intake lumen.
A thermo-resistive sensor can be disposed on the dilatation balloon to monitor the temperature of the lesion. A second thermo-resistive sensor can be disposed on the shaft to provide a control temperature reading.
In another preferred embodiment of the cryoplasty catheter in accordance with the present invention, the cryoplasty catheter includes a shaft having proximal and distal ends. The shaft defines an inflation lumen and a drain lumen therethrough. Each lumen has a proximal and a distal end proximate the proximal and distal ends of the shaft respectively. A dilatation balloon is disposed at the distal end of the shaft and is in fluid communication with the inflation and drain lumens. The cryoplasty catheter also includes a coolant source connected to the proximal end of the shaft in fluid communication with the inflation lumen.
This embodiment of the cryoplasty catheter can also include a thermo-resistive sensor disposed on the dilatation balloon. As well as the thermo-resistive sensor disposed on the balloon, a control sensor can be disposed on the catheter shaft.
A method of performing cryoplasty is also provided which includes the steps of advancing a cryoplasty catheter across a lesion, inflating the dilatation balloon to dilate the lesion, and delivering coolant to the balloon to cool the lesion. To aid in remodeling, the lesion adjacent the balloon can be cooled to between 10xc2x0 C. and xe2x88x9210xc2x0 C. A portion of the lesion adjacent the balloon can also be frozen to kill cells within the lesion which would otherwise promote restenosis. For enhanced effectiveness, freezing may be done by flash freezing the tissue for 20 to 60 seconds. The cells are preferably frozen at a temperature of between xe2x88x9220xc2x0 C. and to xe2x88x9240xc2x0 C.